Biasing for tunnel junction head

ABSTRACT

A tunnel junction sensor with a track width area which balances a ferromagnetic coupling field with an opposed tunneling sense current field generated by a tunneling sense current to achieve biasing of the magnetic moment of the free layer in a tunnel junction head. The ferromagnetic coupling field is generated in the same direction as the magnetic moment of the pinned layer which is in close proximity to the free layer. Absent any external forces, the orientation of the magnetic moment of the free layer aligns with the orientation of the magnetic moment of the pinned layer. For the tunnel junction sensor to work efficiently, the orientation of the magnetic moment of the free layer should be perpendicular to the orientation of the magnetic moment of the pinned layer. To accomplish biasing the magnetic moment of the free layer in the desired direction, the tunneling sense current is directed in the plane of the conductive layer in such a direction parallel to the ABS so as to create a tunneling sense current field antiparallel to the ferromagnetic coupling field. By balancing these two opposed fields, the orientation of the magnetic moment of the free layer may be oriented perpendicular to the orientation of the magnetic moment of the pinned layer. To force the tunneling sense current to flow in the plane of the conducting layer parallel to the track width, a non-conducting layer located between the conductive layer and a lead wherein the lead is preferably a first shield layer of the sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tunnel junction sensor in a tunneljunction head, and more particularly, to biasing the orientation of themagnetic moment in the free layer in the tunnel junction head using acurrent field generated by a tunnel current.

2. Description of the Related Art

A read head employing a read sensor may be combined with an inductivewrite head to form a combined magnetic head. In a magnetic disk drive,an air bearing surface (ABS) of the combined magnetic head is supportedadjacent a rotating disk to write information on or read informationfrom the disk. Information is written to the rotating disk by magneticfields which fringe across a gap between the first and second polepieces of the write head. In a read mode, the resistance of the readsensor changes proportionally to the magnitudes of the magnetic fieldsfrom the rotating disk. When a current is conducted through the readsensor, resistance changes cause potential changes that are detected andprocessed as playback signals in processing circuitry.

One type of read sensor is a tunnel junction sensor. The details oftunnel junction have been described in a commonly assigned U.S. Pat. No.5,650,958 to Gallagher et al., which is incorporated by referenceherein. The tunnel junction sensor is a device comprised of twoferromagnetic layers (i.e., the pinned and free layers) separated by athin barrier layer and is based on the phenomenon of spin-polarizedelectron tunneling. The typical tunnel junction sensor uses free andpinned layers, such as NiFe or CoFe, with a non-magnetic barrier layertherebetween that is thin enough to permit quantum mechanical sensecurrent tunneling to occur through the barrier layer between the freeand pinned layers. The pinned layer has a magnetic orientation pinned byexchange coupling with a pinning layer wherein the pinning layer is madeof antiferromagnetic material with magnetic spins oriented in apredetermined direction. The tunneling phenomenon is electron spindependent, making the magnetic response of the tunnel junction sensor afunction of the relative orientations and spin polarization of theconduction electrons between the free and pinned layers. Ideally, themagnetic moment orientation of the pinned layer should be pinned 90° tothe magnetic moment orientation of the free layer, with the magneticmoment of the free layer being free to respond to external magneticfields such as fields from a rotating magnetic disk. In the absence ofany external fields acting on the free layer, the magnetic moment of thefree layer is parallel to the direction of the pinned layer, due to aferromagnetic coupling therebetween.

From the above it becomes apparent that what is needed is a way ofbiasing the magnetic moment of the free layer such that it is normal tothe magnetic moment orientation of the pinned layer in a tunnel junctionhead in the absence of the external field.

SUMMARY OF THE INVENTION

The present invention is directed to a tunnel junction sensor thatemploys the field generated from a tunneling sense current through oneof the layers to counterbalance a ferromagnetic coupling field exertedon the free layer by the pinned layer. The ferromagnetic coupling fieldis parallel to the direction of the magnetic moment of a pinned layer.Absent any external forces, the orientation of the magnetic moment ofthe free layer is unfortunately parallel to the orientation of themagnetic moment of the pinned layer due to their close proximity. Forthe tunnel junction sensor to work efficiently, the orientation of themagnetic moment of the free layer should be perpendicular to theorientation of the magnetic moment of the pinned layer. To permit adesired orientation of the magnetic moment of the free layer, atunneling sense current is provided that flows parallel to the ABS inthe plane of a conductive layer so as to create a current fieldantiparallel to the ferromagnetic coupling field. By balancing these twoopposed fields, the magnetic moment orientation of the free layer can beperpendicular to the magnetic moment orientation of the pinned layer. Toget the tunneling sense current to flow in the plane of the conductivelayer, as opposed to through the layer, a non-conducting layer isinserted into the structure. This non-conducting layer makes the currentflow in the plane of the desired layer so as to generate the currentfield of sufficient magnitude to counter balance the ferromagneticcoupling field on the free layer.

In one embodiment, the current flows in the plane of a conductive pinnedlayer parallel to the ABS so as to create the desired current field. Thetunnel junction sensor includes a first shield layer, a non-conductiveantiferromagnetic pinning layer with magnetic spins aligned in apredetermined direction, a pinned layer made of conductive ferromagneticmaterial whose magnetic moment orientation is pinned by exchangecoupling with the magnetic spins of the non-conductive antiferromagneticpinning layer. This magnetization also generates a ferromagneticcoupling field in the predetermined direction. The pinned layer and thefirst shield are electrically connected in a location remote from thetrack width area. A non-magnetic barrier layer is positioned between thepinned layer and a free layer. The free layer is made of a ferromagneticmaterial with a magnetic moment orientation initially parallel to thepinned layer due to the ferromagnetic coupling field. The desiredorientation of the free layer is perpendicular to that of the pinnedlayer magnetic moment orientation (i.e., parallel to the ABS).

In another embodiment, similar to the one described above, anon-conductive insulation layer is placed between the first shield layerand a conductive antiferromagnetic (AFM) pinning layer (which is used inplace of the non-conductive pinning layer of the previous embodiment)with magnetic spins aligned in the predetermined direction. The pinninglayer and the first shield are electrically connected remote from thetrack width area. The pinned layer is made of conductive ferromagneticmaterial whose magnetic moment orientation is pinned by exchangecoupling with the conductive antiferromagnetic pinning layer. Thismagnetization causes the pinned layer to exert a ferromagnetic couplingfield on the free layer that is directed perpendicular to the ABS. Anon-magnetic barrier layer is positioned between the pinned layer and afree layer. The free layer is made of a ferromagnetic material with amagnetic moment orientation initially parallel to the magneticorientation of the pinned layer due to the ferromagnetic coupling field.The desired magnetic moment orientation of the free layer isperpendicular to that of the magnetic moment orientation of the pinnedlayer (i.e., parallel to the ABS).

The first and second shield layers may be used as electrodes for thetunnel junction sensor. A tunneling sense current IT flows through thetunnel junction sensor from the second shield toward the first shield inthe track width area, perpendicular to the plane of the films or layers,except the non-conductive layer. As the tunnel current reaches thenon-conductive layer, the current turns and flows in the plane of theadjacent conductive layer and parallel to the ABS (either the pinning orpinned layer) and finally to the first shield which is connected to theconductive layer outside of the track width area. As the current flowsin the plane of the conductive layer, a tunneling sensor current fieldis generated antiparallel to the ferromagnetic coupling field. Both ofthese fields influence the orientation of the magnetic moment of thefree layer. By balancing these two fields, the orientation of themagnetic moment of the free layer can be directed perpendicular to themagnetic orientation of the pinned layer. As the tunnel junction sensoris positioned over a rotating magnetic disk, external magnetic fieldssensed from the rotating disk moves the orientation of the magneticmoment of the free layer up or down, changing the resistance through thetunnel junction sensor. As the direction of the magnetic moment of thefree layer rotates up from the ABS (i.e., going toward the oppositedirection of an exemplary downwardly directed magnetic moment of thepinned layer), the amount of electron tunneling decreases (i.e., theresistance increases). As the direction of the magnetic moment of thefree layer rotates down toward the ABS (i.e., going toward the samedirection as the magnetic moment of the pinned layer) the amount ofelectron tunneling increases (i.e., the resistance decreases). As thetunneling sense current I_(T) is conducted through the sensor, theincrease and decrease of electron tunneling (i.e., increase and decreasein resistance) are manifested as potential changes. These potentialchanges are then processed as readback signals by the processingcircuitry of the disk drive.

Other objects and advantages of the present invention will becomeapparent upon reading the following description taken together with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an exemplary magnetic disk drive;

FIG. 2 is an end view of a slider with a magnetic head as seen in plane2—2 of FIG. 1;

FIG. 3 is an elevation view of the magnetic disk drive wherein multipledisks and magnetic heads are employed;

FIG. 4 is an isometric illustration of an exemplary suspension systemfor supporting the slider and magnetic head;

FIG. 5 is an ABS view of the slider taken along in plane 5—5 of FIG. 2;

FIG. 6 is a partial view of the slider and a piggyback magnetic head asseen in plane 6—6 of FIG. 2;

FIG. 7 is a partial view of the slider and a merged magnetic head asseen in plane 7—7 of FIG. 2;

FIG. 8 is a partial ABS view of the slider taken along plane 8—8 of FIG.6 to show the read and write elements of the piggyback magnetic head;

FIG. 9 is a partial ABS view of the slider taken along plane 9—9 of FIG.7 to show the read and write elements of the merged magnetic head;

FIG. 10 is a view taken along plane 10—10 of FIGS. 6 or 7 with allmaterial above the coil layer and leads removed;

FIG. 11 is a partial air bearing surface (ABS) illustration of oneembodiment of the sensor of the present invention;

FIG. 12 is an exploded view of FIG. 11;

FIG. 13 is a partial ABS illustration of another embodiment of thesensor of the present invention; and

FIG. 14 is an exploded view of FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Magnetic Disk Drive

Referring now to the drawings wherein like reference numerals designatelike or similar parts throughout the several views, FIGS. 1-3 illustratea magnetic disk drive 30. The drive 30 includes a spindle 32 thatsupports and rotates a magnetic disk 34. The spindle 32 is rotated by amotor 36 that is controlled by a motor controller 38. A combined readand write magnetic head 40 is mounted on a slider 42 that is supportedby a suspension 44 and actuator arm 46. A plurality of disks, slidersand suspensions may be employed in a large capacity direct accessstorage device (DASD) as shown in FIG. 3. The suspension 44 and actuatorarm 46 position the slider 42 so that the magnetic head 40 is in atransducing relationship with a surface of the magnetic disk 34. Whenthe disk 34 is rotated by the motor 36 the slider is supported on a thin(typically, 0.05 μm) cushion of air (air bearing) between the surface ofthe disk 34 and the air bearing surface (ABS) 48. The magnetic head 40may then be employed for writing information to multiple circular trackson the surface of the disk 34, as well as for reading informationtherefrom. Processing circuitry 50 exchanges signals, representing suchinformation, with the head 40, provides motor drive signals for rotatingthe magnetic disk 34, and provides control signals for moving the sliderto various circular tracks on the disk. FIG. 4 shows the mounting of theslider 42 to the suspension 44, which will be described hereinafter. Thecomponents described hereinabove may be mounted on a frame 54 of ahousing 55, as shown in FIG. 3.

FIG. 5 is an ABS view of the slider 42 and the magnetic head 40. Theslider has a center rail 56 that supports the magnetic head 40, and siderails 58 and 60. The rails 56, 58 and 60 extend from a cross rail 62.With respect to rotation of the magnetic disk 34, the cross rail 62 isat a leading edge 64 of the slider and the magnetic head 40 is at atrailing edge 66 of the slider.

FIG. 6 is a side cross-sectional elevation view of a piggyback magnetichead 40, which includes a write head portion 70 and a read head portion72, the read head portion employing an pinned spin valve sensor 74 ofthe present invention. FIG. 8 is an ABS view of FIG. 6. The spin valvesensor 74 and insulating gap payer 75 are sandwiched between first andsecond shield layers 80 and 82. The insulating gap layer 75 insulatesthe shields from each other and may be made from aluminum oxide,aluminum nitride or silicone dioxide. In response to external magneticfields, the resistance of the spin valve sensor 74 changes. To determinethe resistance, a tunneling sense current I_(T) is used. The first andsecond shield layers 80 and 82 are employed as leads. As the magneticmoment of the free layer rotates in response to the magnetic field fromthe disk, the resistance of the tunnel junction structure changes,altering the current through the structure. These resistance changes tobe manifested as potential changes. These potential changes are thenprocessed as readback signals by the processing circuitry 50 shown inFIG. 3.

The write head portion 70 of the magnetic head 40 includes a coil layer84 sandwiched between first and second insulation layers 86 and 88. Athird insulation layer 90 may be employed for planarizing the head toeliminate ripples in the second insulation layer caused by the coillayer 84. The first, second and third insulation layers are referred toin the art as an “insulation stack”. The coil layer 84 and the first,second and third insulation layers 86, 88 and 90 are sandwiched betweenfirst and second pole piece layers 92 and 94. The first and second polepiece layers 92 and 94 are magnetically coupled at a back gap 96 andhave first and second pole tips 98 and 100 which are separated by awrite gap layer 102 at the ABS. An insulation layer 103 is locatedbetween the second shield layer 82 and the first pole piece layer 92.Since the second shield layer 82 and the first pole piece layer 92 areseparate layers this head is known as a piggyback head. As shown inFIGS. 2 and 4, first and second solder connections 104 and 106 connectleads from the spin valve sensor 74 to leads 112 and 114 on thesuspension 44, and third and fourth solder connections 116 and 118connect leads 120 and 122 from the coil 84 (see FIG. 10) to leads 124and 126 on the suspension.

FIGS. 7 and 9 are the same as FIGS. 6 and 8 except the second shieldlayer 82 and the first pole piece layer 92 are a common layer. This typeof head is known as the merged magnetic head. The insulation layer 103of the piggyback head in FIGS. 6 and 8 is omitted.

Present Invention

The present invention is directed to a tunnel junction sensor thatemploys the field generated from a tunneling sense current through oneof the layers to counterbalance a ferromagnetic coupling field exertedon the free layer by the pinned layer. The ferromagnetic coupling fieldis parallel to the direction of the magnetic moment of a pinned layer.Absent any external forces, the orientation of the magnetic moment ofthe free layer is parallel to the orientation of the magnetic moment ofthe pinned layer due to a ferromagnetic coupling field due to the closeproximity of the pinned and free layers. To bias the orientation of themagnetic moment of the free layer in the desired direction, a tunnelingsense current is provided that flows parallel to the ABS, in the planeof a conductive layer, so as to create a current field antiparallel tothe ferromagnetic coupling field. By balancing these two opposed fields,the magnetic moment orientation of the free layer can be perpendicularto the magnetic moment orientation of the pinned layer. To get thetunneling sense current to flow parallel to the ABS in the plane of theconductive layer, as opposed to through the layer, a non-conductinglayer is inserted into the structure. This non-conducting layer makesthe current flow in the plane of the desired layer parallel to the ABSso as to generate the current field of sufficient magnitude to counterbalance the ferromagnetic coupling field on the free layer.

FIG. 11 shows one embodiment of the tunnel junction sensor 200 of thepresent invention which includes a first shield 80, a non-conductivepinning layer 205, a pinned layer 210, a barrier layer 215, a free layer220, an isolation layer 225 and a second shield layer 82. Also shown arehard bias layers 221. The hard bias layers are used for free layerstabilization. FIG. 12 is an exploded view of FIG. 11 showing the layersand exemplary desired orientations of the magnetic moment (M_(P)) 250 ofthe pinned layer 210 and the magnetic moment (M_(F)) 255 of the freelayer 220 in the absence of an external field. In this case, themagnetic moment (M_(P)) 250 of the pinned layer 210 is downward (+ydirection), perpendicular to the ABS, the orientation of the magneticmoment (M_(P)) 250 being pinned by interfacial exchange coupling withthe adjacent pinning layer 205. It is generally desirable for optimumperformance that the orientation of the magnetic moment (M_(F)) 255 ofthe free layer 220 be perpendicular to the magnetic moment (M_(P)) 250of the pinned layer 210 (i.e., the moment direction 255 is parallel tothe ABS). But, it is apparent, as shown in FIG. 12, in the absence ofany external magnetic fields, the orientation of the magnetic moment(M_(F)) 255 of the free layer 220 is parallel to the magnetic moment(M_(P) 250, as shown at 260, due to a ferromagnetic coupling field(H_(FC)) 251 in the +y direction. To permit the magnetic moment (M_(F))255 to assume the preferred direction (i.e., perpendicular to themagnetic moment (M_(P)) 250), a magnetic field in the −y direction mustbe generated to counteract the ferromagnetic coupling field (H_(FC))251.

A tunneling sense current I_(T), using spin dependent electrontunneling, flows through the tunnel junction sensor 200, parallel to theABS, with the first and second shield layers 80 and 82 used as leads. Inthe present invention, the tunnel current I_(T) does not flow in the AFMpinning layer 210 because the pinning layer 205 is non-conductive. Thetunnel current I_(T) is diverted 256, in the −z direction in the pinnedlayer 210, to the location where the pinned layer 210 and the firstshield 80 are connected at 201 by the shunt 226 (i.e., away from thetrack width area 202). While the current 256 is flowing in the plane ofthe pinned layer 210 in the −z direction, a tunneling sense currentfield (H_(I)) 257 is generated antiparallel to the ferromagneticcoupling field (H_(FC)) 251. By balancing the tunneling sense currentfield (H_(I)) 257 and the ferromagnetic coupling field (H_(FC)) 251, themagnetic moment (M_(F)) 255 of the free layer 220 is located parallel tothe ABS, as shown by the solid arrow. The electrical connection 201between the pinned layer 210 and the first shield 80 is in an areaoutside the track width area 202 so that the current I_(T) is conductedin the pinned layer 210 parallel to the ABS and parallel to the trackwidth.

The amount of current I_(T) that flows through the sensor is dependenton the relative magnetic directions (M_(P)) 250 and (M_(F)) 255 of thepinned layer and the free layer. As the tunnel junction sensor 200 ispositioned over the magnetic disk 34, the external magnetic fieldssensed from the rotating disk 34 moves the direction of magnetic moment(M_(F)) 255 of the free layer 220 up or down, changing the resistancethrough the tunnel junction sensor 200. As the magnetic moment (M_(F))255 rotates up from the ABS (i.e., going toward the opposite directionof the magnetic moment (M_(P)) 250), the amount of electron tunnelingdecreases (i.e., the resistance increases). As the magnetic moment(M_(F)) 255 rotates down toward the ABS (i.e., going toward the samedirection as the magnetic moment (M_(P)) 250), the amount of electrontunneling increases (i.e., the resistance decreases). As the tunnelcurrent I_(T) is conducted through the sensor 200, the increase anddecrease of electron tunneling (i.e., increase and decrease inresistance) are manifested as potential changes. These potential changesare then processed as readback signals by the processing circuitry shownin FIG. 3.

The first and second shields 80 and 82 are made from a conductivematerial, such as Permalloy which is Ni₈₀Fe₂₀. The pinning layer 205 ismade of non-conductive material. such as nickel oxide (NiO), having athickness range of 50-150 Å, preferably 100 Å. The non-conductivepinning layer 205 has its magnetic spins oriented in a preferreddirection. The pinned layer 210 is made from a ferromagnetic materialsuch as Ni₄₀Fe₆₀/Co or NiFe/Co₃₀Fe₇₀/Co with a thickness of 20-60 Å,preferably 40 Å. The pinned layer 210 is exchange coupled to the pinninglayer 205 such that the orientation of the magnetic moment of the pinnedlayer is in the same direction as the magnetic spins of the pinninglayer.

The pinned layer 210 is in electrical contact with the first shield 80by a conductive shunt 226 that is located outside the track width area202 at a location 201. The track width area 202 is defined by the widthof the ferromagnetic free layer 220. The barrier layer 215 may be madeof aluminum oxide, with a thickness of 10-30 Å, preferably 20 Å. Thefree layer 220 is made from ferromagnetic material such as Co/NiFe orCo/Ni₉₀Fe₁₀/Ni₄₀Fe₆₀ with a thickness of 20-60 Å, preferably 40 Å. Anisolation layer 225, made of Tantalum (Ta) and having a thickness of30-100 Å, preferably 50 Å, is placed between the free layer 220 and thesecond shield layer 82 for the purpose of preventing a magnetic couplingtherebetween. The first and second shields 80 and 82 are used as leadsfor the tunnel junction sensor 200. The inductive write head 70 is thenformed on the tunnel junction read sensor 200 (or read head 72, see FIG.6 or 7). While the above description describes the construction of oneembodiment of the present invention, there are other layers that may beadded to improve the tunnel junction sensor 200.

To fabricate the tunnel junction 200, the first shield 80 is firstdeposited. Next is the AFM pining layer 205 deposited on the firstshield. A via or shunt 226 is patterned in the pining layer 205. Thepinned layer 210 is deposited on the pinning layer 205, with the pinnedlayer 210 making contact with the shield 80 in the via 226. The tunneljunction barrier layer 215 is deposited on the pinned layer 210. Using alift-off technique, the free layer 220 is deposited on the barrier layer215. The hard bias layer 221 and isolation layer 225 are then deposited.The second shield 82 is deposited on the isolation layer 225. Electricalcurrent flows from the second shield 82 to the free layer 220 and thenthe current tunnels to the pinned layer 210 across the barrier 215.Current then flows parallel to the ABS in the pinned layer 210 to thevia 226 and finally reaches the first shield 80 at 201.

FIG. 13 shows another embodiment of the tunnel junction sensor 230. Thissensor 230 is similar to the sensor 200 described above but instead ofthe non-conductive antiferromagnetic pinning layer 205, a non-conductiveinsulation layer 235 is positioned between the first shield 80 and aconductive antiferromagnetic pinning layer 240. FIG. 14 is an explodedview of tunnel junction sensor 230 in FIG. 13 showing the layers andorientations of the magnetic moment (M_(P)) 250 of the pinned layer 210and the magnetic moment (M_(F)) 255 of the free layer 220. Theorientation of the magnetic moment (M_(P)) 250 of the pinned layer 210is in a downward (+y direction) perpendicular to the ABS, the directionof the magnetic moment (M_(P)) 250 being pinned by interfacial exchangecoupling with the adjacent pinning layer 240. In the preferredembodiment, the orientation of the magnetic moment (M_(F)) 255 of thefree layer 220 is perpendicular to the orientation of the magneticmoment (M_(P)) 250 of the pinned layer 210 (i.e., the moment directionis parallel to the ABS). But, in the absence of any external magneticfields, the orientation of the magnetic moment (M_(F)) 255 of the freelayer 220 is parallel to the magnetic moment (M_(P)) 250, as shown at260, due to a ferromagnetic coupling field (H_(FC)) 251 in the +ydirection. To permit the magnetic moment (M_(F)) 255 to assume thepreferred direction (perpendicular to the magnetic moment (M_(P)) 250),a field in the −y direction must be generated to counteract theferromagnetic coupling field (H_(FC)) 251.

A tunneling sense current I_(T), using spin dependent electrontunneling, flows through the tunnel junction sensor 230 in the −xdirection, parallel to the ABS, with the first and second shield layers80 and 82 used as leads. In the present invention, the tunnel currentI_(T) does not flow directly through the tunnel junction 230. Since theinsulation layer 235 is non-conductive, the tunnel current I_(T) isdiverted 258, by the conductive shunt 226 in the −z direction along thetrack width in the plane of the pinning layer 240. While the current 258is flowing in the pinning layer 240 in the −z direction, a tunnelingsense current field (H_(I)) 259 is generated antiparallel to theferromagnetic coupling field (H_(FC)) 251. The electrical connectionbetween the pinning layer 240 and the first shield 80 is provided at alocation 201 remote from the track width area 202 so that the currentI_(T) flows parallel to the ABS and parallel to the track width in thepinning layer 240. By balancing the tunneling sense current field(H_(I)) 259 and the ferromagnetic coupling field (H_(FC)) 251, theorientation of the magnetic moment (M_(F)) 255 of the free layer 220 islocated parallel to the ABS as shown by the solid arrow. The amount ofcurrent I_(T) that flows through the sensor is dependent on the relativemagnetic directions (M_(P)) 250 and (M_(F)) 255 of the pinned layer 210and the free layer 220. As the tunnel junction sensor 230 is positionedover the magnetic disk 34, the external magnetic fields sensed from therotating disk 34 moves the direction of magnetic moment (M_(F)) 255 ofthe free layer 220 up or down, changing the resistance through thetunnel junction sensor 230. As the magnetic moment (M_(F)) 255 rotatesup from the ABS (i.e., going toward the opposite direction of themagnetic moment (M_(P))250), the amount of electron tunneling decreases(i.e., the resistance increases). As the magnetic moment (M_(F)) 255rotates down toward the ABS (i.e., going toward the same direction asthe magnetic moment (M_(P)) 250), the amount of electron tunnelingincreases (i.e., the resistance decreases). As the tunnel current I_(T)is conducted through the sensor 230, the increase and decrease ofelectron tunneling (i.e., increase and decrease in resistance) aremanifested as potential changes. These potential changes are thenprocessed as readback signals by the processing circuitry shown in FIG.3.

The insulation layer 235 may be made of alumina (Al₂O₃) having athickness of 20-60 Å, with a preferred thickness of 40 Å. The pinninglayer 240 may be made of a conductive antiferromagnetic material such asiron manganese (FeMn), having a thickness range of 50-150 Å, preferably100 Å. Other conductive antiferromagnetic materials (AFM) such as nickelmanganese (NiMn), platinum manganese (PtMn), iridium manganese (IrMn),chromium aluminum manganese (CrAlMn) or palladium manganese (PdMn) maybe used for the pinning layer 240. The inductive write head 70 is thenformed on the tunnel junction read sensor 230 (or read head 72, seeFIGS. 6 or 7).

To fabricate the tunnel junction 230, the first shield 80 is firstdeposited. An insulation layer 235 is deposited over the first shield80. A via or shunt 226 is patterned in the insulation layer 235. Next isthe pining layer 240 deposited on the insulation layer 235 with thepinning layer 240 making contact with the shield 80 in the via 226. Thepinned layer 210 is deposited on the pinning layer 240. The tunneljunction barrier layer 215 is deposited on the pinned layer 210. Using alift-off technique, the free layer 220 is deposited on the barrier layer215. A hard bias layer 221 and an isolation layer 225 are thendeposited. The second shield 82 is deposited on the isolation layer 225.Electrical current flows from the second shield 82 to the free layer 220and then the current tunnels to the pinned layer 210 across the barrier215. Current then flows parallel to the ABS in the pinning layer 240 andthe pinned layer 210 to the via 226 and finally reaches the first shield80 at 201.

Clearly, other embodiments and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. While the description of the tunnel junction sensor isdescribed in relation to a magnetic disk drive read/write head, itshould understood that in other applications, the tunnel junction sensormay be used alone or in combination with other devices. Therefore, thedisclosed invention is to be considered merely illustrative and limitedin scope only as specified in the appended claims.

What is claimed is:
 1. A tunnel junction sensor that has a track widthat an air bearing surface (ABS) comprising: a ferromagnetic electricallyconductive free layer; a non-magnetic insulating barrier layer; aferromagnetic electrically conductive pinned layer; the barrier layerbeing located between the free layer and the pinned layer; anantiferromagnetic pinning layer; a ferromagnetic electrically conductivefirst shield layer; the pinning layer being located between the firstshield layer and the pinned layer and exchange coupled to the pinnedlayer so as to pin the pinned layer magnetic moment of the pinned layerin a first direction, which, in turn, exerts a ferromagnetic couplingfield on the free layer in a first direction; the first shield layerhaving an extended portion that extends beyond said track width of thesensor; and one of the pinned layer or the pinning layer beingelectrically connected to said extended portion of the first shieldlayer for enabling a tunneling sense current to flow parallel to the ABSin said one of the pinned layer or the pinning layer for causing atunneling sense current field to be exerted by said one of the pinnedlayer or the pinning layer on the free layer in a second direction thatis antiparallel to said first direction to counter balance theferromagnetic coupling field on the free layer.
 2. The tunnel junctionsensor as claimed in claim 1 further comprising: a non-conductiveinsulation layer being located between the antiferromagnetic pinninglayer and the first shield layer in the track width: and 59theantiferromagnetic pinning layer is electrically conductive and connectsto said extended portion of the first shield layer.
 3. The tunneljunction sensor as claimed in claim 2 wherein the electricallyconductive antiferromagnetic pinning layer is selected from the groupMnFe, NiMn, IrMn, PtMn, CrAlMn and PdMn.
 4. The tunnel junction sensoras claimed in claim 2 wherein the non-conductive insulation layer ismade from alumina (Al₂O₃).
 5. The tunnel junction sensor as claimed inclaim 1 wherein the pinned layer is connected to said extended portionof the ferromagnetic electrically conductive first shield layer beyondthe track width and the antiferromagnetic pinning layer isnon-conductive.
 6. The tunnel junction sensor as claimed in claim 5wherein the non-conductive antiferromagnetic pinning layer is made fromnickel oxide (NiO).
 7. The tunnel junction sensor as claimed in claim 1further comprising: a ferromagnetic electrically conductive secondshield layer; an isolation layer, the isolation layer being locatedbetween the second shield layer and the free layer; and a tunnelingsense current source for applying said tunneling sense current.
 8. Thetunnel junction sensor as claimed in claim 7 wherein the ferromagneticelectrically conductive first and second shield layers are used aselectrical leads.
 9. The tunnel junction sensor as claimed in claim 1wherein the barrier layer has a thickness from 10 Å to 30 Å.
 10. Thetunnel junction sensor as claimed in claim 9 wherein the barrier layeris made from aluminum oxide.
 11. The tunnel junction sensor as claimedin claim 1 wherein the first direction is normal to the ABS.
 12. Amagnetic head assembly that has an air bearing surface (ABS) comprising:a read head that includes: a tunnel junction sensor that has a trackwidth responsive to applied magnetic fields; first and secondelectrically conductive lead layers connected to the tunnel junctionsensor for conducting a tunnel current through the tunnel junctionsensor; the tunnel junction sensor including: ferromagnetic electricallyconductive first and second shield layers; an isolation layer; aferromagnetic electrically conductive free layer; the isolation layerbeing located between the second shield layer and the free layer; anon-magnetic electrically insulating barrier layer; a ferromagneticelectrically conductive pinned layer; the barrier layer being locatedbetween the free layer and the pinned layer; an antiferromagneticpinning layer; the pinning layer being located between the first shieldlayer and the pinned layer and exchange coupled to the pinned layer soas to pin the pinned layer magnetic moment of the pinned layer in afirst direction which, in turn, exerts a ferromagnetic coupling field onthe free layer in a first direction; the first shield layer having anextended portion that extends beyond said track width of the sensor; andone of the pinned layer or the pinning layer being electricallyconnected to said extended portion of the first shield layer forenabling a tunneling sense current to flow parallel to the ABS in saidone of the pinned layer or the pinning layer for causing a tunnelingsense current field to be exerted by said one of the pinned layer or thepinning layer on the free layer in a second direction that isantiparallel to said first direction to counter balance theferromagnetic coupling field on the free layer; a write head including:first and second pole piece layers and a write gap layer; the first andsecond pole piece layers being separated by the write gap layer at theABS and connected at a back gap that is recessed rearwardly in the writehead from the ABS; an insulation stack having at least first and secondinsulation layers; at least one coil layer embedded in the insulationstack; and the insulation stack and the at least one coil layer beinglocated between the first and second pole piece layers.
 13. The magnetichead assembly as claimed in claim 12 wherein the first and secondelectrically conductive lead layers are the electrically conductivefirst and second shield layers.
 14. The magnetic head assembly asclaimed in claim 12 further comprising; a non-conductive insulationlayer being located between the antiferromagnetic pinning layer and thefirst shield layer in the track width; and the antiferromagnetic pinninglayer is electrically conductive and connects to said extended portionof the first shield layer.
 15. The magnetic head assembly as claimed inclaim 14 wherein the electrically conductive antiferromagnetic pinninglayer is selected from the group MnFe, NiMn, IrMn, PtMn, CrAlMn andPdMn.
 16. The magnetic head assembly as claimed in claim 14 wherein thenon-conductive insulation layer is made from alumina (Al₂O₃).
 17. Themagnetic head assembly as claimed in claim 12 wherein the pinned layeris connected to said extended portion of the ferromagnetic electricallyconductive first shield layer beyond the track width and theantiferromagnetic pinning layer is non-conductive.
 18. The magnetic headassembly as claimed in claim 17 wherein the non-conductiveantiferromagnetic pinning layer is made from nickel oxide (NiO).
 19. Themagnetic head assembly as claimed in claim 12 wherein the barrier layerhas a thickness from 10 Å to 30 Å.
 20. The magnetic head assembly asclaimed in claim 19 wherein the barrier layer is made from aluminumoxide.
 21. The magnetic head assembly as claimed in claim 12 wherein thefirst direction is normal to the ABS.
 22. A magnetic disk drive thatincludes at least one magnetic head assembly that has an air bearingsurface (ABS), the disk drive comprising: a read head that includes: atunnel junction sensor that has a track width responsive to appliedmagnetic fields; and first and second electrically conductive leadlayers connected to the tunnel junction sensor for conducting a tunnelcurrent through the tunnel junction sensor; the tunnel junction sensorincluding: ferromagnetic electrically conductive first and second shieldlayers; a ferromagnetic electrically conductive free layer; anon-magnetic electrically insulating barrier layer; a ferromagneticelectrically conductive pinned layer; the free layer being locatedbetween the second shield and the barrier layer and the barrier layerbeing located between the free layer and the pinned layer; anantiferromagnetic pinning layer; the pinning layer being located betweenthe first shield layer and the pinned layer and exchange coupled to thepinned layer so as to pin the pinned layer magnetic moment of the pinnedlayer in a first direction which, in turn, exerts a ferromagneticcoupling field on the free layer in a first direction; the first shieldlayer having an extended portion that extends beyond said track width ofthe sensor; and one of the pinned layer or the pinning layer beingelectrically connected to said extended portion of the first shieldlayer for enabling a tunneling sense current to flow parallel to the ABSin said one of the pinned layer or the pinning layer for causing atunneling sense current field to be exerted by said one of the pinnedlayer or the pinning layer on the free layer in a second direction thatis antiparallel to said first direction to counter balance theferromagnetic coupling field on the free layer; a write head including:first and second pole piece layers and a write gap layer; the first andsecond pole piece layers being separated by the write gap layer at theABS and connected at a back gap that is recessed rearwardly in the writehead from the ABS; an insulation stack having at least first and secondinsulation layers; at least one coil layer embedded in the insulationstack; and the insulation stack and the at least one coil layer beinglocated between the first and second pole piece layers; a housing; amagnetic disk rotatably supported in the housing; a support mounted inthe housing for supporting the magnetic head with its ABS facing themagnetic disk so that the magnetic head is in a transducing relationshipwith the magnetic disk; means for rotating the magnetic disk;positioning means connected to the support for moving the magnetic headto multiple positions with respect to said magnetic disk; and processingmeans connected to the magnetic head, to the means for rotating themagnetic disk and to the positioning means for exchanging signals withsaid at least one magnetic head assembly for controlling movement of themagnetic disk and for controlling the position of said at least onemagnetic head assembly.
 23. The magnetic disk drive as claimed in claim22 wherein the processing means is connected to the first and secondlead layers for applying the tunneling sense current to the sensor. 24.The magnetic disk drive as claimed in claim 23 wherein the processingmeans applies said tunneling sense current.
 25. The magnetic disk driveas claimed in claim 22 wherein the first and second electricallyconductive lead layers are the electrically conductive first and secondshield layers.
 26. The magnetic disk drive as claimed in claim 22further comprising: a non-conductive insulation layer is located betweenthe antiferromagnetic pinning layer and the first shield layer in thetrack width; and the antiferromagnetic pinning layer is electricallyconductive and connects to said extended portion of the first shieldlayer.
 27. The magnetic disk drive as claimed in claim 26 wherein theelectrically conductive antiferromagnetic pinning layer is selected fromthe group MnFe, NiMn, IrMn, PtMn, CrAlMn and PdMn.
 28. The magnetic diskdrive as claimed in claim 26 wherein the non-conductive insulation layeris made from alumina (Al₂O₃).
 29. The magnetic disk drive as claimed inclaim 22 wherein the pinned layer connects to said extended portion ofthe ferromagnetic electrically conductive first shield layer and theantiferromagnetic pinning layer is non-conductive.
 30. The magnetic diskdrive as claimed in claim 29 wherein the non-conductiveantiferromagnetic pinning layer is made from nickel oxide (NiO).
 31. Themagnetic disk drive as claimed in claim 22 wherein the barrier layer hasa thickness from 10 Å to 30 Å.
 32. The magnetic disk drive as claimed inclaim 31 wherein the barrier layer is made from aluminum oxide.
 33. Themagnetic disk drive as claimed in claim 22 wherein the first directionis normal to the ABS.
 34. A method of making a tunnel junction sensorthat has a track width at an air bearing surface (ABS) comprising:forming a ferromagnetic electrically conductive first shield layer;forming an antiferromagnetic pinning layer on the first shield layer;forming a ferromagnetic electrically conductive pinned layer on thepinning layer; forming a non-magnetic electrically insulating barrierlayer on the pinned layer; forming a ferromagnetic electricallyconductive free layer on the barrier layer; the pinning layer beingexchange coupled to the pinned layer so as to pin the pinned layermagnetic moment of the pinned layer in a first direction which, in turn,exerts a ferromagnetic coupling field on the free layer in a firstdirection; the first shield layer having an extended portion thatextends beyond said track width of the sensor; and electricallyconnecting one of the pinned layer or the pinning layer to said extendedportion of the first shield layer for enabling a tunneling sense currentto flow parallel to the ABS in said one of the pinned layer or thepinning layer for causing a tunneling sense current field to be exertedby said one of the pinned layer or the pinning layer on the free layerin a second direction that is antiparallel to said first direction tocounter balance the ferromagnetic coupling field on the free layer. 35.The method as claimed in claim 34 further comprising: forming anon-conductive insulation layer on the first shield layer between thefirst shield layer and the antiferromagnetic pinning layer in the trackwidth; and connecting the antiferromagnetic pinning layer to saidextended portion of the first shield layer wherein the antiferromagneticpinning layer is electrically conductive.
 36. The method as claimed inclaim 35 wherein the electrically conductive antiferromagnetic pinninglayer is selected from the group MnFe, NiMn, IrMn, PtMn, CrAlMn andPdMn.
 37. The method as claimed in claim 35 wherein the non-conductiveinsulation layer is made from alumina (Al₂O₃).
 38. The method as claimedin claim 34 including connecting the pinned layer to said extendedportion of the ferromagnetic electrically conductive first shield layerwherein the antiferromagnetic pinning layer is non-conductive.
 39. Themethod as claimed in claim 38 wherein the non-conductiveantiferromagnetic pinning layer is made from nickel oxide (NiO).
 40. Themethod as claimed in claim 34 further comprising: forming an isolationlayer on the free layer: forming a second shield layer on the isolationlayer; and providing a tunneling sense current source for applying atunneling sense current.
 41. The method as claimed in claim 40 whereinthe ferromagnetic electrically conductive first and second shield layersare used as electrical leads.
 42. The method as claimed in claim 34wherein the barrier layer has a thickness from 10 Å to 30 Å.
 43. Themethod as claimed in claim 42 wherein the barrier layer is made fromaluminum oxide.
 44. The method as claimed in claim 34 wherein the firstdirection is normal to the ABS.
 45. A method of making a magnetic headthat has an air bearing surface (ABS) comprising: forming a tunneljunction sensor that has a track width as follows: forming aferromagnetic electrically conductive first shield layer; forming anantiferromagnetic pinning layer on the first shield layer; forming aferromagnetic electrically conductive pinned layer on the pinning layer;forming a non-magnetic electrically insulating barrier layer on thepinned layer; forming a ferromagnetic electrically conductive free layeron the barrier layer; forming an isolation layer on the free layer;forming a ferromagnetic electrically conductive second shield layer onthe isolation layer; the pinning layer being exchange coupled to thepinned layer so as to pin the pinned layer magnetic moment of the pinnedlayer in a first direction which, in turn, exerts a ferromagneticcoupling field on the free layer in a first direction; the first shieldlayer having an extended portion that extends beyond said track width ofthe sensor; and electrically connecting one of the pinned layer or thepinning layer to said extended portion of the first shield layer forenabling a tunneling sense current to flow parallel to the ABS in saidone of the pinned layer or the pinning layer for causing a tunnelingsense current field to be exerted by said one of the pinned layer or thepinning layer on the free layer in a second direction that isantiparallel to said first direction to counter balance theferromagnetic coupling field on the free layer; and forming a write headas follows: forming a write gap layer and an insulation stack with acoil layer embedded therein on the second shield layer so that thesecond shield layer also functions as a first pole piece for the writehead; and forming a second pole piece layer on the insulation stack andthe write gap and connected at a back gap to the first pole piece. 46.The method as claimed in claim 45 further comprising: forming anon-conductive insulation layer on the first shield layer between thefirst shield layer and the antiferromagnetic pinning layer in the trackwidth; and connecting the antiferromagnetic pinning layer to saidextended portion of the first shield layer wherein the antiferromagneticpinning layer is electrically conductive.
 47. The method as claimed inclaim 46 wherein the electrically conductive antiferromagnetic pinninglayer is selected from the group MnFe, NiMn, IrMn, PtMn, CrAlMn andPdMn.
 48. The method as claimed in claim 46 wherein the non-conductiveinsulation layer is made from alumina (Al₂O₃).
 49. The method as claimedin claim 45 including connecting the pinned layer to said extendedportion of the ferromagnetic electrically conductive first shield layerwherein the antiferromagnetic pinning layer is non-conductive.
 50. Themethod as claimed in claim 49 wherein the non-conductiveantiferromagnetic pinning layer is made from nickel oxide (NiO).
 51. Themethod as claimed in claim 45 further comprising: providing a tunnelingsense current source for applying the tunneling sense current.
 52. Themethod as claimed in claim 51 wherein the ferromagnetic electricallyconductive first and second shield layers are used as electrical leads.53. The method as claimed in claim 45 wherein the barrier layer has athickness from 10 Å to 30 Å.
 54. The method as claimed in claim 53wherein the barrier layer is made from aluminum oxide.
 55. The method asclaimed in claim 45 wherein the first direction is normal to the ABS.